1. Field of the Invention
The present invention relates to control systems for heating apparatus and more particularly for automatic fuel igniting systems in which gaseous fuel is electrically ignited to start the flame used for heating.
2. Description of the Prior Art
The prior art includes examples of fuel igniting systems in which the flame is ignited by electronic flame igniting circuitry and then the flame is sensed by flame sensing circuitry. U.S. Pat. Nos. 3,902,838 and 3,938,937 describe pilot ignition systems in which flame sensing is accomplished using the principle of flame conductivity, and in which sensing of the flame causes de-activation of the spark generating circuitry. U.S. Pat. No. 3,806,305 discloses a spark ignition circuit using voltage multiplication in the spark generating circuitry. All of these prior art systems suffer a similar inadequacy in that no backup is provided for the flame sensing circuitry so that a failure of that circuitry could result in unlit raw gas flow.